Osteoarthritis. Most research on
glucosamine sulfate has measured its
effectiveness on osteoarthritis of the
knee. However, there is some evidence
that it might also help osteoarthritis
of the hip or spine.

Some research suggests that
glucosamine reduces pain of
osteoarthritis in the knee about as
well as the over-the-counter pain
reliever acetaminophen (Tylenol). It
also seems to reduce pain about as
much as the nonsteroidal
anti-inflammatory drugs (NSAIDs)
ibuprofen (Motrin, Advil) and
piroxicam (Feldene). But there is a
difference between glucosamine sulfate
and these drugs in the time it takes
to reduce pain. The NSAIDs, such as
Motrin, Advil, and Feldene, relieve
symptoms and reduce pain usually
within about 2 weeks, but the
glucosamine sulfate takes about 4-8
weeks.

Glucosamine sulfate does not seem to
decrease pain in everyone who takes
it. Some people get no benefit. Some
research shows that glucosamine
sulfate might not work very well for
people with more severe, long-standing
osteoarthritis, or for people who are
older or heavier.

In addition to relieving pain,
glucosamine sulfate might also slow
the breakdown of joints in people with
osteoarthritis who take it long-term.
Some researchers hope that glucosamine
sulfate might keep osteoarthritis from
getting worse as quickly as it
otherwise might. There is some
evidence that people who take
glucosamine sulfate might be less
likely to need total knee replacement
surgery.

When I want to know things related with sports, I use the British Journal of Sports Medicine, keep in mind most of the content is behind a paywall. Fortunately this study on glucosamine is not:

glucosamine supplementation can
provide some degree of pain relief and
improved function in persons who
experience regular knee pain, which
may be caused by prior cartilage
injury and/or osteoarthritis. The
trends in the results also suggest
that, at a dosage of 2000 mg per day,
the majority of improvements are
present after eight weeks.